No time limit will be imposed on the search for MH370 because the world deserves to know what happened, Australian premier Tony Abbott said Monday, as a ship equipped to locate the plane's "black box" prepared to set sail.

The hunt for physical evidence that the Malaysia Airlines jet crashed in the Indian Ocean more than three weeks ago has turned up nothing, despite a massive operation involving seven countries and repeated sightings of suspected debris.

Abbott said the search across an expanse of ocean the size of Norway would continue for as long as necessary to track down the Boeing 777, which was carrying 239 people when it vanished on March 8 en route from Kuala Lumpur to Beijing.

"I'm certainly not putting a time limit on it... We can keep searching for quite some time to come," Abbott told reporters at the Perth military base coordinating the operation.

"We owe it to the families, we owe it to everyone that travels by air, we owe it to the anxious governments of the countries who had people on that aircraft. We owe it to the wider world which has been transfixed by this mystery for three weeks now."

More than a dozen Chinese relatives of those aboard the ill-fated plane -- part of a group of nearly 30 who arrived in Malaysia to press authorities for answers -- kept up the pressure on Monday during a visit to a Buddhist temple on the outskirts of Kuala Lumpur.

Wearing T-shirts that read "MH370 come back safely" in Mandarin, they lit candles and left flowers at the temple in an hour-long prayer session for loved ones. But their anger at Malaysia's handling of the crisis still smoldered.

"We will never forgive those who hurt our families and don't tell the truth and delay the rescue mission," a spokesman for the group told reporters, reiterating the belief among many relatives of the 153 Chinese aboard that Malaysia has concealed the truth.

'Critical' to find debris

The Australian vessel Ocean Shield, fitted with a device known as a towed pinger locator and an underwater drone equipped with electronic sensors for detecting the black box's signal, was to conduct sea trials off Perth on Monday before heading to the search area.

Captain Mark Matthews from the US Navy said it was "critical" to first locate a likely crash site.

"Right now the search area is basically the size of the Indian Ocean, which would take an untenable amount of time to search," he said.

A black box signal usually lasts only about 30 days. Fears have been mounting that it could already be too late, with Ocean Shield needing up to three days to get to the search area.

However, Matthews said the black box signal could last up to 15 days longer than thought.

Once any floating debris is confirmed to be from the plane, authorities plan to work backwards -- analysing recent weather patterns and ocean currents -- to a possible crash site.

Families demand answers

Malaysia believes MH370 was deliberately diverted by someone on board, but nothing else is known. It has said satellite data indicates the plane went down in seas far off western Australia.

The circumstances have brought pilot Zaharie Ahmad Shah, 53, and co-pilot Fariq Abdul Hamid, 27, under intense scrutiny, but no evidence has emerged to implicate them, and family and acquaintances have attested their good character.

Zaharie's daughter Aishah on Monday accused a British tabloid newspaper, the Daily Mail, of concocting a report "out of thin air" alleging that her father was "disturbed" due to marital trouble.

"May god have mercy on your souls," she told the paper in a Facebook posting quoted by local media.

Many Chinese relatives, already distraught and angry, have been further incensed by Malaysian Prime Minister Najib Razak's announcement on March 24 that the plane was lost at sea, saying that could not be concluded until wreckage is found.

But Abbott backed Najib's conclusion, saying it was supported by an "absolutely overwhelming wave of evidence".

A source close to Malaysia's investigation told AFP that authorities in Kuala Lumpur were upset with "the Chinese side whipping up the families' emotions against Malaysia".

China's state media have regularly heaped scorn on Malaysia for losing MH370, and Beijing has pressed for more transparency in its investigation.

Monday's search saw 10 planes take to the skies, with ten ships already at sea. Australia, China, Japan, New Zealand, Malaysia, South Korea and the US are taking part.

Malaysia remains officially in charge of the search, but Australia has assumed increasing responsibility, appointing retired air chief marshal Angus Houston to head a new coordination centre in Perth.